Coal and other solid organic fuels are gasified to obtain a high calorific fuel gas used as a fuel gas or a source gas. Conventional gasification of coal or the like is performed at a high temperature of about 1273 K (1000° C.) or more, and in order to maintain the high temperature, combustion of some of the fuel such as coal is needed by supplying air or the like to combust some of the fuel such as coal or the like. As a result, a calorific value per unit volume of a produced gas may be decreased by mixing an exhaust gas due to the combustion therewith.
At the same time, since fuel conversion efficiency from the fuel to the produced gas is decreased, necessary fuel per calorific value of the gasified gas is increased, and operating cost needed for the gasification is increased. In addition, in recent times, while gasification using high purity oxygen instead of air has been performed in order to maximally increase the calorific value of the produced gas, in this method, since equipment for manufacturing oxygen is needed, equipment cost and operating cost are further increased.
Development of a technique of performing gasification at a low temperature is performed as a method of solving these problems. When the gasification is performed at the low temperature, consumption of air or oxygen can be reduced, and an increase in calorific value of the produced gas and a corresponding increase in fuel conversion efficiency are expected.
However, when the gasification is performed at the low temperature, a large amount of tar is generated in the produced gas, and the conversion efficiency of the fuel into the produced gas is decreased by the content of the tar. In addition, when the produced gas is used as a raw material for chemosynthesis, the tar should be removed.
A method of cleaning the produced gas with water and other solvents is generally employed in the related art as a method of removing the tar in the produced gas.
However, in the method of cleaning the gas with a solvent such as water, a large amount of drainage or waste liquid is generated, and the drainage or waste liquid should be processed. In addition, while the tar has a calorific value and can be used as fuel, it is difficult to recover the tar from the cleaned waste liquid, and accordingly, utilization efficiency of the fuel is decreased by the content of the tar.
In order to solve the problems, reforming the produced gas after the low temperature gasification at a high temperature and further decomposing the tar into CO, H2 or the like to use them has been considered (see Patent Document 1 or the like).
In addition, a gasification device in which, as a chemical such as limestone (CaCO3) is supplied into a combustion furnace filled with a bed material and an oxidant (air) is supplied to combust char supplied from a gasification furnace, heating of the bed material and burning (activation) of the chemical are performed, and as the bed material and the active chemical of the high temperature are supplied into a gas purifying furnace, the tar of the produced gas introduced into the gas purifying furnace from the gasification furnace is reformed by an catalytic action of the active chemical, is disclosed (see Patent Document 2 or the like).